Oxidation resistant carbonaceous bodies and method for making



J ly 1966 w. E. PARKER ETAL 3,261,697

OXIDATION RESISTANT CARBONACEOUS BODIES AND METHOD FOR MAKING Filed Jan. 16, 1962 3 Sheets-Sheet 1 CUMULATIVE WEIG HT LOSS- GRAMS 4 6 8 IO I2 l4 TIME HOURS EFFECT OF B 8, CONCENTRATION ON REACTIVITY AT 700C.

INVENTORJS WILLIAM E. PARKER BYJOHN F. RAKSZAWSKI w mm mw ATTORNEYS July 19, 1966 REACTION RATE" g-/hr./g.

OXIDATION RESISTANT CARBONACEOUS BODIES AND METHOD FOR MAKING Filed Jan. 16, 1962 5 Sheets-Sheet 2 HEAT TREATMENT TEMPERATURE C.

OXIDATION RATES OF SAMPLES CONTAINING BORON SILICIDES AFTER HEAT TREATMENT TO VARIOUS TEMPERATURES N0 ADDITIVE 0.1 MOLE 7 8 8 1.0 MOLE I- S 0.| MOLE 7 5 5.

INVENTORS WILLIAM E. PARKER JOHN F. RAKSZAWSKI ifl mmi $001.0 ZIJIQULW ATTORNEYS 5 Sheets-Sheet 3 W. E. PARKER ETAL July 19, 1966 OXIDATION RESISTANT CARBONACEOUS BODIES AND METHOD FOR MAKING Filed Jan. 16. 1962 3 2 WEE zoFBEm INVENTORS WILLIAM E. PARKER JOHN F. RAKSZAWSKI BY ATTORNEYS REACTION TEMPERATURE I/K x I0 EFFECT OF OXIDATION TEMPERATURE ON RATE OF OXIDATION o |5oo BLANK :1 z5oo BLANK 0 500 0.1 MOLEV. B 8 A 25oo o.| MoLE7- B S United States Patent 3,261,697 OXIDATION RESISTANT CONACEOUS BODIES AND METHOD FOR MAKING William E. Parker, Lewiston, and John F. Ralrszawski,

Niagara Falls, N.Y., assignors to Air Reduction Company, Incorporated, a corporation of Delaware Filed Jan. 16, 1962, Ser. No. 166,563 4 Claims. (Cl. lilo-56) This invention relates to oxidation resistant carbonaceous bodies and to methods for making carbonaceous articles which are resistant to oxidation.

Carbon and graphite articles are widely used as electrodes and in a variety of other high temperature applications. Such high temperature use may be in the atmosphere, or in the presence of other materials which oxidize the carbonaceous material. Various additives, coatings, impregnants, and treatments have been proposed to reduce the burning of carbonaceous materials under high temperature operating conditions. Some of these practices improve the resistance to oxidation of the carbonaceous materials at low and moderate temperatures, but the effectiveness is lost in whole or in part after the materials have been subjected to high temperatures. These prior art procedures increase the cost of the carbonaceous articles and all are of limited eiiectiveness. The problem of inhibiting oxidation of carbon and graphite articles has remained a serious one.

It is an object of this invention to produce carbon and graphite bodies that exhibit improved oxidation resistance characteristics by reason of containing boron silicides.

Another object of the invention is to produce carbon and graphite bodies that have improved resistance to oxidation by adding boron silicides to the green mix from which the bodies are formed.

The addition of the boron silicides causes the carbon and graphite bodies to be more resistant to oxidation and thereby permits more efficient and economical use in high temperature applications where oxidation normally would be a problem.

It is a further object of this invention to produce carbon and graphite bodies which are resistant to oxidation at high temperatures and which do not lose their oxidation resistance by treatment at high temperatures.

It is also an object of this invention to provide new and improved methods of producing carbon and graphite bodies which have high oxidation resistance.

Other objects and advantages of the invention will become apparent as the description of the invention proceeds.

In the drawings, FIGURES 1, 2 and 3 graphically present test data which will be described hereinafter.

Carbon and graphite specimens containing boron silicides were prepared and tested to determine resistance to oxidation in comparison with carbon and graphite specimens containing no boron silicides. Two methods were used to prepare carbon and/ or graphite bodies containing boron silicides as oxidation inhibitors.

FIRST METHOD OF PREPARATION Powdered tetraboron silicide, 13 8i, or hexaboron silicide, B Si, was blended with spectroscopic graphite 3,261,697 Patented July 19, I966 The cumulative weight loss was recorded as a function of time and the oxidation rate in grams per hour per gram was measured. The data for these initial oxidation determinations are shown in Table I.

Table I.-0xidation rates of spectroscopic graphite samples containing 0.1 mole percent boron silicide additive 1 Sample was given a 17 hour preheat at 1,200 C. in helium prior to oxidation.

These data show that when either B Si or B Si was added to the spectroscopic graphite the oxidation rate was reduced by a factor of about 2. The data from Table I indicates that the purity and particle size of the boron silicides, at least for the conditions measured, are not critical. Preheating in helium for 17 hours at 1200 C. does enhance the oxidation inhibition to some extent. On a mole percent basis, B Si is a slightly better oxidation inhibitor, but on a weight percent basis, B Si is more efiective.

The effect of boron silicide concentration was investigated by oxidizing, at 700 C., samples prepared from spectroscopic graphite and B Si (325 mesh). The preparation of the samples was identical to that described above. The results are shown in Table II and in FIGURE 1.

Table II.-E]ject of boron silicide concentration on initial oxidation of spectroscopic graphite at 700 C.

Initial Mole Percent Weight Oxidation BnSi Percent BaSi Rate,

g. /hr. lg.

None None 0. 101

0. 001 0. 0079 0. 0895 0. 01 0.079 0. 0815 0.05 0.38 0. 0675 0. 10 0. 79 0. 0645 1. 0 7. 3 0. 0538 5. 0 29. 0 None 10. 0 46. 3 None 20. 0 65. 9 None SECOND METHOD OF PREPARATION In the second method used to prepare carbon and graphite samples containing boron silicides, conventional carbon (generic) fabricating techniques were used. Four mixes were prepared. Each contained 2465 gms. of 60 X 200 mesh petroleum coke and 740 gms. of 12 mesh coal tar pitch. The amounts of boron silicides used are shown in Table III. Mix No. l was used as a control so that the effects of B Si and B Si could be measured.

The following procedure was used in incorporating the additive. The coke and pitch (and boron silicide, when used) were blended together at room temperature and the remainder of the mixing, molding and baking to 900 C. was carried out by conventional techniques.

Further heat treatments of individual bars were made in an induction furnace to temperatures of 1500, 2000", 2500, and 3000 C. in a flowing argon atmosphere. Those carbon bars heated to temperatures in excess of 2200 C. become graphite or graphitized carbon as is well known in the art and as discussed in the Kirk- Othmer Encyclopedia of Chemical Technology, vol. 3, p. 21, copyright 1949 by The Interscience Encyclopedia, Inc. Oxidation rates were obtained by reacting in air (5000 cc./min.) at 700 C. The experimental results are presented in Table IV and in FIGURE 2. The Mix Nos. in Table IV are the same as in Table III.

Table IV.Oxidation rates of conventional samples containing boron silicides after heat treatment to various temperatures Oxidation Rate, g./l1r./g., After Heat Treatment to- Mix N0.

000 C. 1,500 C. 2,000 C. 2,500 C. 3,000 C.

Table V.-Efiect of oxidation temperature on rate of oxidation Oxidation Rate, g./l1r./g., at Reaction Temperature of Sample 700 C. 800 C. 900 C. 1,000 C.

1,500 0. blank 2. 42 2. 40 2. 3.17 1,500 O. 0.1 mole percent B 1 0. 292 1. 45 2. 67 3. 11 2,500 C. blank 1. 99 2. 71 3. 20 2. 61 2,500 O. 0.1 mole percent Bssl 0.124 0. 747 2. 03 2. 63

After heat treating to 1500 C., the inhibition does not occur at reaction temperatures of 900 C. or 1000 C. Heat treatment to 2500 C. extends the inhibiting efiect to an oxidation temperature of 900 C.

This invention is of particular significance in that it makes use of compounds to be used as oxidation inhibitors which do not lose their effectiveness after high thermal treatments. In fact, some thermal treatment appears to enhance the inhibiting effect. Because of this, the compounds can be used by simply incorporating them into the green mix followed by conventional processing procedures. No additional treatments are necessary.

The test data demonstrates that the addition of boron silicides produces carbon and graphite articles which exhibit substantially improved resistance to oxidation and which have greater durability under oxidizing conditions than previously known carbon and graphite articles. These desired results are attained without impairment of other properties of the carbon and graphite articles.

What is claimed is:

1. An article made of carbon and having a low rate of oxidation upon exposure to oxidation conditions at temperatures of 700 C. and above, which article consists of graphitized carbon having homogeneously distributed therein 0.001 to 20 mole percent of a boron silicide.

2. The article according to claim 1 in which the boron silicide is from the group consisting of tetraboron silicide and hexaboron silicide.

3. The article according to claim 1 in which the boron silicide is tetraboron silicide.

4. The article according to claim 1 in which the boron silicide is hexaboron silicide.

References Cited by the Examiner UNITED STATES PATENTS 2,013,625 9/1935 Buck 106-56 FOREIGN PATENTS 456,602 11/1936 Great Britain.

TOBIAS E. LEVOW, Primary Exaimner.

JOHN H. MACK, Examiner.

I. POER, Assistant Examiner. 

1. AN ARTICLE MADE OF CARBON AND HAVING A LOW RATE OF OXIDATION UPON EXPOSURE TO OXIDATION CONDITIONS AT TEMPERATURES OF 700*C. AND ABOVE, WHICH ARTICLE CONSISTS OF GRAPHITIZED CARBON HAVING HOMOGENEOUSLY DISTRIBUTED THEREIN 0.001 TO 20 MOLE PERCENT OF A BORON SILICIDE. 